This invention relates to the transmission, reception, detection, synchronization, and use of ultra-wideband communication systems. In particular, it pertains to a continuous noise transmitted-reference, delayed hopped (TR/DH) ultra-wideband radio communications system.
Conventional ultra-wideband (UWB) radio systems operate by transmitting and receiving a sequence of very short radio frequency (RF) pulses, the duration of which is typically less than a nanosecond. This is referred to as impulse radio. The individual pulses typically have low energy. Consequently, the low duty cycle of the pulsed waveform results in a very low average power.
One conventional approach to implementing UWB communications systems is to utilize a pulse position modulation (PPM) scheme to impress information onto a UWB carrier. PPM is an orthogonal signaling scheme by which a receiver determines in which one of a number of different time windows a received pulse appears, and this determination conveys a quantum of information, e.g., if there are two possible time windows, determination of one window conveys one bit of information; for three windows, a trit of information is conveyed, for four windows, two bits, and so on.
Successful operation of a PPM system requires accurate time synchronization be acquired and maintained between transmitter and receiver. For example, for an UWB PPM system, this synchronization must be accurate to within a fraction of the pulse duration. Because the pulse duration is quite small in a UWB system, the synchronization requirements are quite stringent. The time required to establish synchronization for this method can be prohibitive, and acquisition is not always possible in the presence of multiple access interference, which occurs when more than one pair of transmitters and receivers is active at the same time. A long acquisition time is a major risk in the use of conventional UWB impulse radio communications. Therefore, a need exists for UWB communication systems without the synchronization difficulties associated with conventional approaches.